1. Field of the Invention
This invention relates to a new process for the production of compounds containing blocked alcoholic hydroxyl groups and, optionally, free hydroxyl groups and to the use of compounds containing in all at least three such groups for the production of polyurethanes.
2. Description of the Prior Art
It is generally known that reactive systems which can be stored at room temperature and converted into high molecular weight polyurethanes under the effect of heat can be produced by mixing organic polyhydroxyl compounds containing preferably alcoholically bound hydroxyl groups with blocked polyisocyanates (cf. for example Houben-Weyl, Methoden der organischen Chemie, Vol. XIV/2, 4th Edition, Georg Thieme Verlag, Stuttgart 1963, pages 61-70). The disadvantage of this process, however, lies in the fact that volatile and, in many cases, even inflammable and physiologically harmful substances, i.e. the blocking agents used for blocking the isocyanate groups, are released during the thermal hardening of systems of the type in question. In addition, the use of systems such as these in coating compositions is attended by the disadvantage that the coating cannot be chemically dried, for example by the reaction of free isocyanate groups with atmospheric moisture, because the systems are largely inert even to atmospheric moisture at temperatures below the hardening temperature.
Accordingly, the object of the present invention is to provide new systems which are not attended by the disadvantages of conventional systems based on blocked polyisocyanates and free polyhydroxyl compounds, i.e. can be thermally converted into high molecular weight polyurethanes without the elimination of readily volatile blocking agents despite virtually indefinite storage at room temperature, and which by virtue of the presence of free isocyanate groups under "chemical drying" under the influence of atmospheric moisture before the actual thermal crosslinking process.
It has now surprisingly been found that this object can be achieved by combining the polyisocyanates containing free isocyanate groups of the type normally encountered in polyurethane chemistry with certain compounds containing blocked alcoholic hydroxyl groups obtained by the process described in detail hereinafter.
The compounds containing blocked alcoholic hydroxyl groups and, optionally, also free alcoholic hydroxyl groups obtained by the process according to the invention described in detail hereinafter are not only suitable for the above-mentioned application, they are also fungicidally active substances--this applies in particular to the products based on monohydric alcohols obtained by the process according to the invention--or high molecular weight, often rubber-like polymers which may be split up into their monomeric constituents by simple heating--this applies in particular to products based on polyhydric alcohols and at least difunctional N,N'-disubstituted 5-acyliminoimidazolidine diones obtained by the process according to the invention.